Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


S Maganti

#14155

double sided boards - process / design issue. | 22 September, 1998

We are getting into a lot of double sided boards offlate. Our customer is loading a lot of RNETS, Diodes ( MINLS, SOT23s and other 2 leaded diodes ). We are processing it through a traditional glue process and wave soldering the SMT parts along with the PTH parts, I am getting a lot of solder shorts on 50 mil devices and skips on the diodes. Have you guys had any problem like this, if so please respond. My customer has a serious real estate problem, he cannot move devices to the component side due to this reason. Thanks in advance

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Chrys

#14156

Re: double sided boards - process / design issue. | 22 September, 1998

| We are getting into a lot of double sided boards offlate. Our customer is loading a lot of RNETS, Diodes ( MINLS, SOT23s and other 2 leaded diodes ). We are processing it through a traditional glue process and wave soldering the SMT parts along with the PTH parts, I am getting a lot of solder shorts on 50 mil devices and skips on the diodes. | Have you guys had any problem like this, if so please respond. | My customer has a serious real estate problem, he cannot move devices to the component side due to this reason. | Thanks in advance Wow, shorts and skips together. Feast AND famine! Not like you can even try to strike a balance! You're really bummin' now. Just kidding. ;-) A dumb question - are the parts oriented correctly to minimize shadowing and bridging? And do the RNETs have solder thieve pads? If your layout is correct, then you gotta look at the process. The chip wave is meant to splash solder everywhere to eliminate skips. So, if you're getting skips, turn the chip wave up. Now, a chip wave alone would create a bazillion shorts. The smooth wave, on the other hand, fills holes and debridges all the skips made by the chip wave. Without a debridging knife, the height of the smooth wave is absolutely critical to eliminating shorts. The smoother the smooth wave is, the better the natural advantage of the surface tension at peel off to snap those shorts clean. So, you could be running the smooth wave too high and not getting a nice peel off. Easy fix; turn it down. Or, the machine could need cleaning (!!!!!) Set the wave height to barely reach the top of the fingers and look at the wave. Is it really smooth? Or does it look a little ripple-y towards the center? If it looks a little ripple-y, it's probably time to chisel some of the dross out of those flow ducts to get the laminar flow back. If you need to squeak out to the end of the week before breaking out the torch & chisel, try raising the pot as far as possible and running a lower pump speed. Your wave should smooth out a little. Good luck, Chrys

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